Radiohead's previous albums include The Bends and Kid A

Artists must have had a top 75 UK single or album during the past 16 months before they can be considered.

But Radiohead album In Rainbows was only released for download on the band's website, which does not report sales to chart compilers.

Prince album Planet Earth was given away free in a newspaper. Chart rules stated it was ineligible for inclusion.

In other circumstances, Radiohead would have been in the running for the best British group and best British album shortlists.

A spokesman for the group said they had not expected to be included in the nominations.

Prince could have been up for best international male solo artist and best international album.

Prince recently performed for 21 nights at London's O2 arena

Radiohead released the download version of In Rainbows in October. Fans were invited to put their own price on the 10 audio files that made up the album.

Radiohead rejected press reports that claimed two-thirds of downloaders paid nothing - but did not reveal their own figures.

The band will release the CD and vinyl versions of the album on 31 December, meaning it will be eligible for inclusion for 2009's Brit Awards, presuming it enters the top 75 of the album chart.

An estimated three million copies of Prince's CD were distributed with the Mail on Sunday in July.

Public vote

The Brit Awards will be hosted live by Ozzy and Sharon Osbourne from Earls Court in London on 20 February.

Most of the Brit nominees and winners are voted for by an academy of 1,000 people, ranging from music critics and industry experts to student representatives.

Winners in four categories are chosen by the public.

British breakthrough act will be chosen by BBC Radio 1 listeners and the British live act will be voted for by Radio 2 listeners.